Field of the Invention
The present invention relates to a color correction apparatus, a display apparatus, and a color correction method.
Description of the Background Art
An additive process of mixing three primary colors, such as red, green, and blue, to produce various colors is performed in liquid crystal display apparatuses. Thus, tone values indicating three respective primary-color amounts are input to the liquid crystal display apparatus that displays a color according to the three input tone values.
However, in a case where a gradual change in all or some of the three input tone values does not smoothly change a display color, the display color looks unnatural to an observer who is observing it. This problem is significant particularly in the tone of white.
For this reason, γ characteristics that indicate a relationship between a tone value indicating a primary-color amount of input primary color and brightness of primary color components of a display color are corrected to smoothly change the display color when all or some of the three tone values gradually change.
The γ characteristics are often corrected according to a lookup table. The lookup table defines tone conversion characteristics and includes a plurality of input tone values for indexes and a plurality of output tone values respectively corresponding to the plurality of input tone values. When the γ characteristics are corrected according to the lookup table, the tone conversion is performed on pre-tone-conversion tone values according to the lookup table. The tone conversion specifies an output tone value corresponding to an input tone value that coincides with the pre-tone-conversion tone value, and sets a post-tone-conversion tone value to the specified output tone value.
When one lookup table common to all three primary colors is prepared, and the γ characteristics are corrected according to the one prepared lookup table, the tone conversion is performed on each of three pre-tone-conversion tone values according to the one lookup table. In this case, a ratio of the three post-tone-conversion tone values cannot be made different from a ratio of the three pre-tone-conversion tone values, so that the color cannot be corrected.
It has been proposed that three lookup tables corresponding to respective three primary colors are prepared, and the γ characteristics are corrected according to the three prepared lookup tables so as to correct the color. In this case, the ratio of the three post-tone-conversion tone values can be made different from the ratio of the three pre-tone-conversion tone values, so that the color correction can be performed on white. However, the color correction cannot be properly performed on any color depending on characteristics of the liquid crystal display apparatus.
The color correction according to a three-dimensional lookup table has been proposed so as to properly perform the color correction on any color regardless of the characteristics of the liquid crystal display apparatus. The three-dimensional lookup table includes a plurality of groups each of which is a group of input tone values and a plurality of groups each of which is a group of output tone values. The latter groups respectively correspond to the former groups for indexes. For the color correction according to the three-dimensional lookup table, the tone conversion is performed on three tone values according to the three-dimensional lookup table. The tone conversion specifies a group of the output tone values corresponding to a group of the input tone values that coincides with a group of pre-tone-conversion tone values, and sets a group of post-tone-conversion tone values to the specified group of the output tone values. In one example, International Publication No. WO2009/101802 and Japanese Patent Application Laid-Open No. 2002-016939 each disclose the techniques.
In the liquid crystal display apparatus, a frame image needs to be displayed immediately after an input of a signal that expresses the frame image. Thus, the processing on the signal that includes the color correction needs to be performed in real time. Therefore, the three-dimensional lookup table is preferably installed in hardware for the color correction according to the three-dimensional lookup table.
For the conventional color correction according to the three-dimensional lookup table, however, the three-dimensional lookup table needs to hold 2563×3=50,331,648 bits of correction data to cover all combinations of the three tone values that are each expressed by a bit string of 8 bits. This requires many resources to install the three-dimensional lookup table in the hardware. It is thus unrealistic to install the three-dimensional lookup table in the hardware.
A distance between lattice points in the three-dimensional lookup table can be increased to reduce the correction data in order to reduce the necessary resources. When the distance between the lattice points is increased to reduce the correction data, however, the γ characteristics and colors may not be properly corrected between the lattice points.
These problems also arise when the correction is performed in other than the liquid crystal display apparatus.